The proposed studies in this application are directed toward obtaining a better understanding of the mechanisms of infection of implanted cardiovascular prostheses. Our hypothesis is that material surface interactions with flowing blood lead to alteration of basic pathophysiologic mechanisms which increase athe probability of bacterial interaction and subsequent infection. The approach considers the importance of the material surface, the blood, the blood flow, and the bacteria in the development of cardiovascular prosthesis infections. The studies emphasize the use of clinically derived human materials, i.e., blood and bacteria, and clinically relevant cardiovascular materials coupled with controlled in vitro systems to systematically and comprehensively elucidate infection mechanisms with controlled in vitro systems to systematically and comprehensively elucidate infection mechanisms with cardiovascular prostheses. The overall goals of the project are to; 1) characterize in a comprehensive fashion blood and bacterial surface interactions with cardiovascular materials, 2) determine the similarities and differences in the thrombogenesis mechanisms and infection mechanisms which lead to infections in cardiovascular prostheses with special emphasis on the synergistic effects of material surface thrombosis and bacterial adhesion and colonization, and 3) to develop new design strategies for infection and thrombosis-resistant cardiovascular materials. Our experimental approach utilizes the variable shear stress rotating disk system to determine interactions important in human blood protein/platelet/leukocyte interactions with Staphylococcus epidermidis and biomaterials. Quantification of bacterial interactions will be accomplished using high rsolution fluorescence microscopy, laser confocal microscopy and atomic force microscopy. In addition to slime-producing S. epidermidis (RP62A), adhesion deficient S. epidermidis transposon mutants will be created, characterized and utilized. The effect of adsorbed blood proteins, fibrin(ogen), von Willebran Factor, and complement components iC3b, Factor h and Factor D, on bacterial adhesion int he presence of cellular elements will be determined. Platelet receptor (GPIIb/IIIa and P- selectin) and activation studies will be carried out to further elucidate platelet/bacteria/biomaterial adhesion. Leukocyte (PMN) and monocyte adhesion and activation on biomaterials, as mediated by plasma proteins and complement activation, in the presence of S. epidermidis under variable shear stress will be characterized and correlated with leukocyte receptor expression (CD11/CD180, cell activation markers (enzymes), and cell function assays (R01, phagocytosis, chemotaxis and microbial killing).